JLG M4069 ANSI Service Manual - Manual (Page 76)

SECTION 4 - HYDRAULICS
4-4 – JLG Lift – 3121122
selected, remaining until a function switch and both direc-
tions are no longer selected.
When the controller is returned to neutral, the controller
will control smooth stopping of the machine, using plug
braking, before the brake is allowed to operate.
NOTE: Depressing the lift function switch while driving will
not interrupt drive function.
Pump Motor (LIft)
Pump motor drive will start only if the following conditions
are satisfied:
1. Accelerator in neutral position.
2. Traction mode off (brake applied).
3. Depress lift select. the lights indicating lift select at
the platform control will flash. The accelerator must
be moved within 3 seconds after the lift light illumi-
nates.
NOTE: Depressing the drive function switch while lifting will
not interrupt lift function.
Any time brushes are being replaced in a drive motor
or pump motor, all brushes in the motor should be
replaced.
4.8 FEATURES
Traction Mode
NOTE: The lift up and drive functions are proportional.
The drive function is fully proportional with automatic
speed cutback above elevation. The system is designed
for maximum traction to be delivered to both wheels at all
times.
Machines equipped with oscillating axle will have oscilla-
tion below elevation cutback speed only.
4.9 CYLINDER CHECKING PROCEDURES
NOTE: Cylinder checks must be performed any time a cylin-
der component is replaced or when improper system
operation is suspected.
Cylinder Without Counterbalance Valves
(Steer)
1. Using all applicable safety precautions, activate
hydraulic system and fully extend cylinder to be
checked. Shut down hydraulic system.
2. Carefully disconnect hydraulic hose from retract port
of cylinder. There will be initial weeping of hydraulic
fluid which can be caught in a suitable container.
After initial discharge, there should be no further
leakage from the retract port.
3. Activate hydraulic system, and activate cylinder
extend function.
4. If cylinder retract port leakage is less than 6-8 drops
per minute, carefully reconnect hose to retract port
and retract cylinder. If leakage continues at a rate of
6-8 drops per minute or more, cylinder repairs must
be made.
5. With cylinder fully retracted, shut down motor and
carefully disconnect hydraulic hose from cylinder
extend port.
6. Activate hydraulic system and activate cylinder
retract function. Check extend port for leakage.
7. If extend port leakage is less than 6-8 drops per
minute, carefully reconnect hose to extend port,
then activate cylinder through one complete cycle
and check for leaks. If leakage continues at a rate of
6-8 drops per minute or more, cylinder repairs must
be made.
Cylinders With Single Counterbalance Valve
(Lift Cylinder)
OPERATE ALL FUNCTIONS FROM GROUND CONTROL STATION
ONLY.
1. Using all applicable safety precautions, activate
hydraulic system.
2. Raise platform completely and place a suitable over-
head lifting device approximately 1 in (2.5 cm) below
the platform.
3. After completing the above, shut down hydraulic
system and allow machine to sit for 10-15 minutes.
This is done to relieve pressure in the hydraulic
Table 4-1. Cutout Heights
Function M3369/3369LE M4069/4069LE
Elevated Cutback Height
8 ft - 9 ft 6 in
(2.4 m - 2.9 m)
9 ft 6 in - 11 ft 8 in
(2.9m - 3.6m)
Drive Cutout Height N/A
28 ft - 30 ft
(8.5 m - 9.1m)